Series pumps still gets my vote, and those quad-splitters kind of make me cringe from how restrictive they look. I also imagine that trying to get a system to bleed with one of those at the t-line/fillport junction would be a right pain in the ass.

If you really want to run two loops, is having two fillports that difficult to implement in your particular system? It would take the uncertainty out of the equation, and make it easier to work on individual components.